1. Field of the Invention
The present invention relates to a vibration-generating stepping motor which is equipped with a bearing functioning as a magnetic circuit, so that miniaturization of the motor can be performed, the strength of the bearing can be maintained, and strong magnetomotive force, that is, desired rotation speed can be produced.
2. Description of Related Art
In recent years, in mobile devices (for example, mobile phones, personal handyphone systems (PHSs), and personal digital assistants (PDAs)), vibration-generating motors are used for call-reception informing functions or for providing vibration sensations. An inexpensive DC (Direct Current) motor with a brush may be used as a vibration-generating motor. However, the service life of the DC motor is short. Since time periods for starting and stopping of the motor are long, it is difficult to control the DC motor. Thus, a stepping motor, which has a relatively long service life, has a simple drive circuit, can be easily controlled, and is advantageous as a vibration-generating motor.
Japanese Unexamined Patent Application Laid-open No. 2004-215397 has proposed a technique for a vibration-generating motor. This vibration-generating motor is an inner rotor type of PM (Permanent Magnet) stepping motor which is equipped with two rotor magnets. The rotor magnets are provided as a first magnet and a second magnet at different positions with respect to a shaft in an axial direction. An eccentric weight, which shifts a gravity center of a rotor, is provided between the two rotor magnets. This vibration-generating motor is equipped with two bearings in the same manner as the two rotor magnets, so that a biased load received by the bearing can be reduced, and the service life of the bearing can be extended.
The sizes of mobile devices (for example, Mobile phones, PHSs, and PDAs) are progressively reduced, and vibration-generating motors provided in the above devices are made more compact and thinner.